Optical storing apparatus

Abstract

A control unit positions a laser beam toward a target track on a medium on the basis of a tracking error signal (TES) Y indicative of a positional deviation amount from a track center as a zero point on the basis of return light from the medium. A position signal correcting unit executes a correcting arithmetic operation using a non-linear function such as a quadratic polynomial, a quadratic monomial equation, or the like to the TES Y and outputs a corrected TES Z obtained by correcting detection sensitivity characteristics to desired characteristics so that a feedback is sufficiently performed when a lead-in control to the track center by the control unit is executed.

What is claimed is:  
     
       1. An optical storing apparatus comprising: 
       a pickup for moving an irradiating position of a laser beam to an arbitrary track position on a medium;  
       an information signal processing unit for reproducing at least information to said medium by said laser beam;  
       a position signal detecting unit for detecting a position signal Y according to a positional deviation amount X in which a track center of fie medium is set to 0 on the basis of return light of said laser beam from the medium;  
       a position signal correcting unit for outputting a corrected position signal Z obtained by correcting detection sensitivity characteristics for said positional deviation amount to desired characteristics by performing a correcting arithmetic operation using a predetermined non-linear function on the basis of said position signal Y; and  
       a positioning control unit for performing control such that said laser beam is moved toward a target track of said medium and the laser beam is lead-n controlled to the center of the target track by switching a control mode to a position servo control at a position just before the target track and the laser beam is allowed to trace the target track after completion of the lead in control, wherein said corrected position signal Z is used for at least one of said lead-in control and said tracing of said target track.  
     
     
       2. An apparatus according to  claim 1 , wherein said position signal correcting unit defines an ideal position signal Z desired  as a desired position signal for an actual positional deviation amount X of said laser beam, executes a correcting arithmetic operation using a predetermined non-linear function to said position signal Y, and outputs the corrected position signal Z which is approximated to or coincided with said ideal position signal Z desired . 
     
     
       3. An apparatus according to  claim 2 , wherein when an absolute value of the position signal Y detected by said position signal detecting unit is equal to or larger than a predetermined threshold value Y th , said position signal correcting unit executes a correcting arithmetic operation using a predetermined non-linear function to said position signal Y, thereby calculating the corrected position signal Z. 
     
     
       4. An apparatus according to  claim 2 , wherein said position signal correcting unit sets an Nth order polynomial 
       
         
           Z=a N Y N +a N−1 Y N−1 + . . . +a 2 Y 2 +a 1 Y+a 0    
         
       
       as said non-linear function and substitutes said position signal Y into said Nth order polynomial, thereby calculating the corrected position signal Z. 
     
     
       5. An apparatus according to  claim 2 , wherein when a threshold value Y th  of a positive value is set to a predetermined value which is equal to or smaller than a maximum amplitude of the position signal Y, 
       said position signal correcting unit calculates said corrected position signal Z by  
       
         
           Z=K YZ ·Y  
         
       
        in a range (|Y|≦Y th ) where an absolute value |Y| of said position signal Y is equal to or smaller than the  
       threshold value Y th , 
       calculates the corrected position signal Z by substituting said position signal Y into an Nth order polynomial  
       
         
           Z=a N Y N +a N−1 Y N−1 + . . . +a 2 Y 2 +a 1 Y+a 0    
         
       
        in a range (Y th <Y) where said position signal Y exceeds said threshold value Y th  of a positive value, and  
       calculates the corrected position signal Z by substituting said position signal Y into an Nth order polynomial  
       
         
           Z=−(a N |Y| N +a N−1 |Y| N−1 + . . . +a 2 Y 2 +a 1 |Y|+a 0 )  
         
       
        in a range (Y<−Y th ) where said position signal Y is smaller than said threshold value −Y th  of a negative value.  
     
     
       6. An apparatus according to  claim 4 , wherein said position signal correcting unit calculates the corrected position signal Z by substituting said position signal Y into a quadratic polynomial 
       
         
           Z=a 2 Y 2 +a 1 Y+a 0    
         
       
       in a range (Y th <Y) where said position signal Y exceeds a threshold value Y th  of a positive value, and 
       calculates the corrected position signal Z by substituting said position signal Y into a quadratic polynomial  
       
         
           Z=−(a 2 Y 2 +a 1 |Y|+a 0 )  
         
       
        in a range (Y<−Y th ) where said position signal Y is smaller than said threshold value −Y th  of a negative value.  
     
     
       7. An apparatus according to  claim 2 , wherein said position signal correcting unit uses linear characteristics of 
       
         
           Z desired =K XZ ·X  
         
       
       as said ideal position signal Z desired . 
     
     
       8. An apparatus according to  claim 2 , wherein as said ideal position signal Z desired , said position signal correcting unit uses linear characteristics of 
       
         
           Z desired =K XZ ·X  
         
       
       in a range (|X|≦X th ) where an absolute value |X| of said positional deviation amount X lies within a threshold value X th , 
       uses non-linear characteristics of  
       
         
           Z desired =K XZ ·X+K NL (X−X th ) n    
         
       
        in a range (X th <X) where said positional deviation amount X exceeds said threshold value X th  of a positive value, and, further,  
       uses non-linear characteristics of  
       
         
           Z desired =−{K XZ ·|X|+K NL (|X|−X th ) n}   
         
       
        in a range (X<−X th ) where said positional deviation amount X is smaller than said threshold value −X th  of a negative value.  
     
     
       9. An apparatus according to  claim 1 , wherein the non-linear function in said position signal correcting unit is prepared as a table and a correction is executed by referring to said table. 
     
     
       10. An apparatus according to  claim 1 , wherein said position signal correcting unit sets an Nth order monomial equation as said non-linear function and substitutes said position signal Y into said Nth order monomial equation, thereby calculating the corrected position signal Z. 
     
     
       11. An apparatus according to  claim 10 , wherein when a threshold value Y th  is set to a value (Y max ·K th ) obtained by multiplying a maximum amplitude Y max  of the position signal Y by a positive coefficient K th  of 1 or smaller, 
       said position signal correcting unit calculates said corrected position signal Z by  
       
         
           Z=Y  
         
       
        in a range (|Y|≦Y th ) where an absolute value |Y| of said position signal Y is equal to or smaller than the threshold value Y th ,  
       calculates the corrected position signal Z by substituting said position signal Y into an Nth order monomial equation  
       
         
           Z=Y N /Y th   (N−1)    
         
       
       in a range (Y th <Y) where said position signal Y exceeds said threshold value Y th  of a positive value, and 
       calculates the corrected position signal Z by substituting said position signal Y into an Nth order monomial equation  
       
         
           Z=−|Y| N /Y th   (N−1)    
         
       
        in a range (Y<−Y th ) where said position signal Y is smaller than said threshold value −Y th  of a negative value.  
     
     
       12. An apparatus according to  claim 11 , wherein said position signal correcting unit calculates the corrected position signal Z by substituting said position signal Y into a quadratic monomial equation 
       
         
           Z=Y 2 /Y th    
         
       
       in a range (Y th <Y) where said position signal Y exceeds said threshold value Y th of a positive value and 
       calculates the corrected position signal Z by substituting said position signal Y into a quadratic monomial equation  
       
         
           Z=−Y 2 /Y th    
         
       
        in a range (Y<−Y th ) where said position signal Y is smaller than said threshold value −Y th  of a negative value.  
     
     
       13. An apparatus according to  claim 10 , wherein said position signal correcting unit calculates the corrected position signal Z by substituting said position signal Y into a cubic monomial equation 
       
         
           Z=Y 3 /Y th   2    
         
       
       in a range (Y th <Y) where said position signal Y exceeds a threshold value Y th  of a positive value and calculates the corrected position signal Z by substituting said position signal Y into a cubic monomial equation 
       
         
           Z=−|Y| 3 /Y th   2    
         
       
        in a range (Y<−Y th ) where said position signal Y is smaller than said threshold value −Y th  of a negative value.